1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a laser beam printer and the like, and more particularly, it relates to an image forming apparatus having a recording material bearing member for conveying a recording material to a position where a toner image is formed on the recording material.
2. Related Background Art
An image forming apparatus in which a toner image is formed on a recording material, an image forming technique wherein a recording material is borne on a recording material bearing member and a toner image is formed on the recording material while the recording material bearing member is being moved has been proposed. Particularly, this technique is frequently applied to a color copying machine wherein toner images having different colors are superimposed on a recording material to obtain a full-color image. An example of such a color copying machine is shown in FIG. 6.
In a color copying machine shown in FIG. 6, an electrostatic latent image is formed on a photosensitive drum 50 by illuminating light corresponding to image information onto the photosensitive drum which has been charged positively or negatively, by means of an exposure means 51. The latent image is developed by a developing means 52 as a toner image which is in turn transferred onto a recording medium 53. In order to successively transfer a plurality of toner images onto the recording medium 53, the recording medium 53 is wound around a transfer drum (recording medium bearing member) 54 and the plural toner images are successively transferred onto the recording medium 53 while the transfer drum 54 is being rotated.
In order to utilize the resources effectively in such a color copying machine, it is desirable to form the toner images on both surfaces of the recording medium. In this case, it is considered that, after the toner is transferred to the surface of the recording medium 53, the recording medium 53 is sent by a convey means (not shown) to a fixing means where the toner image is fixed to the recording medium, and then the recording medium is wound around the transfer drum 54 again so that a new toner image can be transferred onto the other surface of the recording medium 53.
On the other hand, in fixing devices for fixing a toner image to a recording material such as fixing devices which comprise a fixing roller and a pressure roller and in which a toner image is fixed to a recording material by heat and pressure while the recording material is being moved by these rollers, oil is generally coated on the roller or rollers to prevent the offset of toner. Accordingly, once the toner image is fixed to the recording material, the oil is adhered to the recording material.
In order to form the toner images on both surfaces of the recording material, when the recording material to which the oil was adhered is wound around the transfer drum again, the oil is also adhered to a peripheral surface of the transfer drum. As a result, the oil will also be adhered to a peripheral surface of the photosensitive drum contacted with the peripheral surface of the transfer drum. If the oil is adhered to the photosensitive drum, due to the viscosity of the oil, the toner will not be transferred from the photosensitive drum to the recording material or the toner will be adhered to an area of the photosensitive drum to which the toner is not normally adhered. Consequently, an output image becomes thinner than a desired image or the fog occurs in the output image. Particularly, in apparatuses for forming a color image, since a larger amount of oil is required to prevent the offset of toner in comparison with apparatus for forming a mono-color image, the reduction in density of the output image or the fog is apt to occur.
On the other hand, the toner adhered to non-image forming areas of the photosensitive drum, i.e., areas on the peripheral surface of the photosensitive drum between images (formed on the drum) or areas on the photosensitive drum disposed outside the image forming area in a generatrix direction of the drum will also be transferred from the photosensitive drum to the transfer drum. Accordingly, when the function capable of forming the toner images on both surfaces of the recording material is added to the image forming apparatus, before the oil is transferred from the peripheral surface of the transfer drum to the peripheral surface of the photosensitive drum, the oil mixed with the toner must be removed from the peripheral surface of the transfer drum.
The oil mixed with the toner may be removed by using a fur brush or a web-shaped cloth. However, the oil cannot be removed completely by the fur brush alone; whereas, when the web is used alone, the service life of the web is very short because the toner is adhered to the web, and, thus, the web cannot be put to the practical use. Thus, it is considered that both the fur brush and the web are used simultaneously.
However, in order to remove the toner adhered to the transfer drum, it is necessary to slidingly contact the fur brush with the recording material bearing member with high relative speed, so that the scraped toner is apt to be scattered (in a direction A in FIG. 6). Although it is considered that a peripheral surface of the fur brush 55 is enclosed by a cover 56 to prevent the scattered toner from spreading (FIG. 6), since the cover 56 should not be contacted with the transfer drum, the toner is scattered through a clearance between the cover and the transfer drum. If the web is enclosed by a cover similarly, since there is clearance between the cover and the transfer drum, it is impossible to completely prevent the toner scattered from the fur brush from being adhered to the web.